Interesting how the bottom DO got down near 6 a couple of times this past fall. That's plenty of oxygen, and obviously there is even more above that. However, even in your groundwater-fed, moderately fertile pit pond, there obviously is some decomposition happening. Aquatic plants dying? Phytoplankton? Tree leaves?
I believe that most of the decomp is from aquatic plants dying off. Very few leaves would enter the pond as there are no trees other than shoreline willows nearby. I am sure that Phytoplankton contribute as well at a lesser degree than the aquatic plants. Aquatic plants are now present in 60 percent of the pond and this year was a bumper crop year for them.
